1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling an access network discovery and selection function and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple UEs, and communicates with a core network (e.g., evolved packet core (EPC) network) including a mobility management entity (MME), a serving gateway, etc., for Non Access Stratum (NAS) control.
Besides, a closed subscriber group (CSG) is defined in the 3GPP standards, for managing CSG cells (e.g., femto cells). In detail, each CSG cell is identified by a CSG identity, and multiple CSG cells may share a same CSG identity. The UE can determine whether it can access a CSG cell (e.g., communicate with the EPC network via the CSG cell) by checking a CSG identity of the CSG cell. Further, a CSG cell can be configured to operate in a CSG mode, to allow only a limited set of UEs to access the CSG cell. Alternatively, a CSG cell can be configured to operate in an open access mode, to allow all UEs to access the CSG cell.
An access network discovery and selection function (ANDSF) is a new network entity located (e.g., operated) in a home public land mobile network (PLMN) of a UE as a Home-ANDSF (H-ANDSF), or in a visited PLMN of the UE as a Visited-ANDSF (V-ANDSF). The ANDSF is used for providing assistance data of network discovery and selection according to operators' policy. The ANDSF shall respond to a request transmitted by a UE for accessing network discovery information (pull mode operation), or initiate data transfer to the UE (push mode operation), according to network triggers or a result of previous communications with the UE. In detail, an inter-system mobility policy (ISMP), provided by the ANDSF, is used for describing operator-defined rules and preferences that may affect inter-system mobility decisions taken by the UE. For example, when the UE intends to route IP traffic only over a single radio interface, the inter-system mobility policy can be considered, to decide when inter-system mobility is allowed (or restricted) and/or to select an access technology type and/or an access network which is the most preferable. On the other hand, an inter-system routing policy (ISRP), provided by the ANDSF, is used for describing inter-system routing policies according to which the UE can route IP traffic over multiple radio interfaces simultaneously. For example, the UE can decide whether an access technology type and/or access network is restricted to a specific IP traffic flow and/or a specific APN. The UE may also select an access technology type and/or an access network which is the most preferable.
Therefore, the ANDSF can provide ISMP policies to a UE, for assisting the UE to perform network discovery and selection according to operators' policies. Further, the ANDSF provides the ISMP policies for a preferred access technology to the UE under that validityArea provides location information including PLMN, LAC, TAC, GERAN_CI, UTRAN_CI, EUTRA_CI, etc. For example, when the UE is a specific CSG member and located in coverage of a macro EUTRA cell and a group of CSG cells with a specific CSG identity, the ANDSF can only provide routing policies in favor of a PrioritizedAccess between a 3GPP access technology and non-3GPP access technologies (e.g., WLAN with a SSID) or between cells in the 3GPP access technology under that the ValidityArea provides a specific cell identity.
However, a home access network scenario is not considered in the prior art. In detail, if the UE enters coverage of a group of CSG cells with the same CSG ID, the ANDSF can only provide a list of routing policies with ValidityArea configured to each cell ID. The routing policies are valid only when the UE is using a cell with a cell ID specified in the validityArea. Handling of the routing policies is complicated and is not necessary. Further, the UE may be in coverage of multiple CSG cells with different CSG IDs, wherein some of the CSG cells may have different capabilities. The ANDSF does not allow an operator to provide a routing policy with a preferred access technology configured as the 3GPP access technology with a specific CSG ID.
On the other hand, when the UE is handed over from a Macro cell to a CSG cell, an existing packet data network (PDN) connection of the UE remains connecting to a PDN gateway (P-GW) in an EPC network via a home eNB according to the prior art. If a home network equips with a local gateway (L-GW), the ANDSF lacks an applicable leaf for providing offloading policies to the UE, so as to route PDN connections of the UE from the P-GW in the EPC network to the L-GW in the home network.
Besides, according to the prior art, an operator uses ISRP to influence a UE to select between a 3GPP access technology and non-seamless (NS) WLAN offload, for routing a specific PDN connection associated to a specific APN) according to multi access PDN connectivity (MAPCON) polices or NS-WLAN offload policies, or routing specific IP flows according to IP Flow Mobility and Seamless Offload (IFOM) policies.
However, when the UE has multiple PDN connections, the ANDSF lacks applicable leafs for providing offloading policies to the UE, for the UE to select a specific IP interface identified by associated APN for routing specific IP flows. For example, the UE has multiple PDN connections via the same access network to the EPC network (e.g., PDN1 associated with APN1 for evolved packet system (EPS) services and PDN2 associated with APN2 for IP multimedia subsystem (IMS) services) or the home network (e.g., PDN1 associated with APN1 via the EPC network and PDN2 associated to APN2 via the L-GW in the home Network). Based on the current ISRP policies, there is no routing policy according to which the UE can route a specific PDN connection or a specific IP flow in the above scenarios.
Therefore, how to solve abovementioned problems is a topic to be discussed and addressed.